The reading of electrical energy, water flow, and gas usage has historically been accomplished with human meter readers who came on-site and manually documented meter readings. Over time, this manual meter reading methodology has been enhanced with walk by or drive by reading systems that use radio communications to and from a mobile collector device in a vehicle. Recently, there has been a concerted effort to accomplish meter reading using fixed communication networks that allow data to flow from the meter to a host computer system without human intervention.
Automated systems, such as Automatic Meter Reading (AMR) and Advanced Metering Infrastructure (AMI) systems, may use radio frequency (RF) signals to collect data from transponders attached to meters that measure usage of resources, such as gas, water and electricity. AMR systems use a mobile data collector, such as a handheld computer equipped with RF technology or a vehicle-based RF system, to collect meter data. In this document, terms such as “mobile interrogator”, “interrogator” and “mobile device” will be used to refer to a mobile data collection platform. Such systems may employ a number of different infrastructures for collecting this meter data from the meters. For example, some automated systems obtain data from the meters using a fixed wireless network that includes, for example, a central node, e.g., a collection device, in communication with a number of endpoint nodes (e.g., meter reading devices (MRDs) connected to meters). At the endpoint nodes, the wireless communications circuitry may be incorporated into the meters themselves, such that each endpoint node in the wireless network comprises a meter connected to an MRD that has wireless communication circuitry that enables the MRD to transmit the meter data of the meter to which it is connected. The wireless communication circuitry may include a transponder that may or may not be uniquely identified by a transponder serial number. The endpoint nodes may either transmit their meter data directly to the central node, or indirectly though one or more intermediate bi-directional nodes that serve as repeaters for the meter data of the transmitting node.
Some networks may employ a mesh networking architecture. In such networks, known as “mesh networks,” endpoint nodes are connected to one another through wireless communication links such that each endpoint node has a wireless communication path to a central node. This central node may be commonly referred to by several names including: gatekeeper; collector; and network access point. In this document, terms such as “gatekeeper” and “collector” will most often be used to refer to this functionality. One characteristic of mesh networks is that the component nodes can all connect to one another via one or more “hops.” Due to this characteristic, mesh networks can continue to operate even if a node or a connection breaks down. Accordingly, mesh networks are self-configuring and self-healing, significantly reducing installation and maintenance efforts.
Data collection systems such as electric, gas, and water utility systems tend to fall into two classifications: fixed or mobile network. Each has advantages and disadvantages. A fixed network typically has a tree structure with endpoints at the extreme ends of the tree. These endpoints relay their data toward a central head end by passing data first through a local area network (LAN) including other endpoints, repeaters, and collectors, and then through a wide area network (WAN) to the head end. Data gathered by the head end may be analyzed, stored, presented and/or forwarded to other utility and consumer systems. Some units, such as electricity meters, in a fixed network are always on. Other units, such as gas meters, water meters, and in-home modules, are battery operated and may periodically receive a wake-up signal to tie into the network. This periodic wake-up process can be unilateral at the discretion of the endpoint or the result of a wake-up process initiated by adjacent always-on devices.
A mobile network can be drive-by, fly-by, or walk-by in nature and typically involves a mobile interrogator traveling a predetermined route to gather data from endpoint devices in residential and commercial locations. The mobile interrogator may also issue commands to the endpoint devices. The endpoint devices may include water, gas, and electricity metering and control devices, such as thermostats and load control devices. There is typically little or no communication between endpoint devices themselves, and each endpoint device typically maintains its own history of data for the past collection period. The mobile interrogator wakes up the endpoint devices for the communication exchange. Alternatively, the devices may unilaterally transmit their data periodically so that the mobile interrogator can receive the data whenever it travels by. The collected data is passed from the mobile interrogator to a route manager, and then up to a head end that interfaces to a utility billing system.
When power outages occur in an electric system, connected meters with automated meter reading (AMR) functions may lose their reference clock. Even when local battery power is available, long duration outages can extend beyond the capability of the local battery power source to maintain clock operations. Because modern meter automation systems use a variety of calendar and schedule-based events, this loss of reference time can be critical.